Wastewater treatment has always been important, particularly for water containing human waste, which can spread dangerous diseases. Traditional methods of dealing with human waste include indoor toilets, municipal sewage systems, septic tanks, and other such systems and infrastructure. These systems serve the important functions of removing human waste from living areas and transporting it to facilities where it can be disposed of or treated.
Human waste can become problematic when the normal facilities for waste removal and treatment are unavailable. This might occur after a natural disaster or political upheaval. In these situations, the normal waste removal systems such as sewers may be disrupted, leaving the population to find other ways to dispose of waste. Disposing of human waste directly into the environment without any treatment can lead to the spread of disease. In disaster situations, problems with the spread of disease can be compounded by scarcity of resources such as water, electricity, and fuel.
More sanitary methods of disposing of waste include digging latrines and using portable toilets with waste storage tanks. However, these solutions have the disadvantages of unpleasant odors and a limited capacity. Portable toilets with storage tanks can only hold a finite amount of waste before they must be transported to a location where the waste can be disposed of safely.
An anaerobic digestion process is a fermentation process which has been used to treat organic waste such as human waste, livestock waste, and sewer sludge. See U.S. Pat. No. 4,491,522. Through anaerobic digestion, organic matter is partially removed from wastewater by converting at least some of the organic matter into biogas. Anaerobic digestion has been accomplished through the use of bioreactors into which wastewater is fed. One particular type of bioreactor, called an induced sludge blanket reactor, induced bed reactor, or IBR, is disclosed in U.S. Pat. No. 7,452,467, which is incorporated in its entirety into this application. IBRs are often installed near farms or other facilities that produce large amounts of organic waste. They are installed as permanent fixtures, often with a small building enclosing them. As used herein, the term “anaerobic digester” refers to a reactor in which a pretreated substance can be placed and anaerobic organisms are allowed to convert the pretreated substance into bioenergy. As used herein, the term anaerobic digester encompasses “partially-anaerobic digesters” which are similar to an anaerobic digester; however, the reactor may be specifically designed to accommodate mixed cultures of aerobic and anaerobic organisms. The anaerobic and aerobic organisms can include, but are not limited to archaea, bacteria, yeast, fungi, plant cells, animal cells and genetically-engineered organisms which are selected for their ability to bioconvert the substrate and produce a selected product. Non-limiting examples of anaerobic and partially-anaerobic digesters include: anaerobic activated sludge process, anaerobic clarigester, anaerobic contact process, anaerobic expanded-bed reactor, anaerobic filter, anaerobic fluidized bed, anaerobic lagoon, anaerobic migrating blanket reactor, batch system anaerobic digester, continuous stirred-tank reactor (CSTR), expanded granular sludge bed digester, hybrid reactor, Imhoff tank, induced blanket reactor, internal circulation reactor (IC), one-stage anaerobic digester, partial mixing anaerobic digester, submerged media anaerobic reactor, two-stage anaerobic digester, upflow anaerobic sludge blanket, upflow and down-flow anaerobic attached growth digester, etc.
One useful aspect of anaerobic digestion is its ability to produce biogas. Biogas is a methane-rich product of anaerobic digestion, produced by bacteria as they break down the organic matter in a bioreactor. Biogas can be used as a fuel, to provide on-site heating or electricity generation. As a consequence of the digestion process, biogas can contain high concentrations of hydrogen sulfide, carbon dioxide, and water. Downstream utilization of the methane produced from the digestion process has been hindered by the high concentrations of these impurities. For example, use of unpurified biogas to drive engine turbines can quickly lead to corrosion (e.g., pitting) of the turbine or other engine components. Biogas has been purified through a method disclosed in the U.S. patent application entitled “Off Gas Purification,” (Pub. No. US 2011/0041689 A1) which is incorporated in its entirety into this application. After being purified, the biogas is much more useful for applications such as heating and electricity generation.